Propulsion unit and vessel comprising the propulsion unit

ABSTRACT

Disclosed is a propulsion unit for propelling a vessel. The propulsion unit comprises a main body configured to be arranged at a keel of the vessel and comprising a pivot point, a fin being movably arranged in relation to the main body, and an actuator assembly for generating a heave motion of the fin in relation to the main body. The actuator assembly comprises at least one actuator. The fin is connected to the pivot point, such that the fin is arranged to pivot around the pivot point when the at least one actuator generates the heave motion of the fin, thereby generating a pitch motion of the fin.

The present disclosure pertains to the field of propulsion systems forvessels. The present disclosure relates to a propulsion unit for avessel and vessel comprising the propulsion unit.

BACKGROUND

The field of propulsion systems for vessels is concerned with convertingenergy output from a vessel's prime mover into forward motion. Dependingon the type of vessel and service provided by the vessel, fuel costs mayrepresent as much as 50-60% of total ship operating costs. A screwpropeller is the mainly used propulsion device on vessels today. Maximumachievable open-water efficiencies by modern screw propellers are about70%. For commercial shipping, it is desirable to improve the efficiencyof the propulsion system, to avoid wasting the energy provided by theprime mover.

SUMMARY

Accordingly, there is a need for a propulsion system, which mitigates,alleviates or addresses the shortcomings existing and provides a moreefficient propulsion of a vessel.

Disclosed is a propulsion unit for propelling a vessel. The propulsionunit comprises a main body configured to be arranged at a keel of thevessel and comprising a pivot point, a fin being movably arranged inrelation to the main body, and an actuator assembly for generating aheave motion of the fin in relation to the main body and/or the keel.The actuator assembly comprises at least one actuator. The fin isconnected to the pivot point such that the fin is arranged to pivotaround the pivot point when the at least one actuator generates theheave motion of the fin, thereby generating a pitch motion of the fin.

It is an advantage of the present disclosure that the fin produces lesshydrodynamic drag than common propulsion systems, such as propellersdriven by shafting moving in the water. The actuator of the propulsionunit provides a driving mechanism for generating the motion of the finwhich is simple and efficient and reduces energy losses and maintenancerequirements of the propulsion unit. The motion of the fin may furtherbe controllable by means of the actuator, such that the hydrodynamiccharacteristics of the fin may be adapted to improve efficiency of thefin. Furthermore, the main body of the propulsion system providesdirectional stability to a vessel comprising the propulsion unit.Thereby, the efficiency of the propulsion unit is increased.

Disclosed is a vessel comprising the propulsion unit for propelling thevessel, as disclosed herein. The main body is arranged to the keel ofthe vessel. The fin is configured to perform a pitch motion and/or aheave motion in relation to the keel of the vessel.

It is an advantage of the present disclosure that the propulsion systemof the vessel increases efficiency and reduces maintenance requirementscompared to common propulsion systems, such as propellers driven byshafting moving in the water. Thus, a fuel consumption of the vessel anddowntime due to maintenance of the vessel may be reduced, which reducesoperating costs and emissions of the vessel. Furthermore, the main bodyof the propulsion system provides directional stability to a vesselcomprising the propulsion unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present disclosurewill become readily apparent to those skilled in the art by thefollowing detailed description of exemplary embodiments thereof withreference to the attached drawings, in which:

FIG. 1A illustrates an exemplary perspective view of a propulsion unitcomprising a single actuator according to this disclosure,

FIG. 1B illustrates an exemplary side view of the propulsion unitcomprising the single actuator according to this disclosure,

FIG. 2A-2D illustrate an exemplary overall design and motion pattern ofa propulsion unit comprising a first actuator and a second actuatoraccording to this disclosure,

FIG. 3 illustrates an exemplary connection for connecting the fin to thefirst and second actuators according to this disclosure,

FIG. 4 illustrates an exemplary main body of the propulsion unitaccording to this disclosure,

FIG. 5 is an exemplary graph illustrating a motion pattern of a fin ofthe propulsion system when the first and second actuators are operatedwith a phase shift according to this disclosure,

FIG. 6 illustrates an exemplary propulsion unit for being rotatablyarranged to a vessel according to this disclosure

FIG. 7 illustrates a perspective outside view of an exemplary vesselcomprising an exemplary propulsion unit according to this disclosure,

FIG. 8 illustrates a perspective inside view of an exemplary vesselcomprising an exemplary propulsion unit according to this disclosure,

FIG. 9 illustrates an exemplary propulsion unit comprising a first and asecond actuator being arranged to the fin via fixed pivot pointsaccording to this disclosure,

FIG. 10 illustrates an exemplary propulsion unit comprising a first anda second actuator being arranged to the fin via fixed pivot pointsaccording to this disclosure, and

FIG. 11 is an exemplary graph illustrating a motion pattern of the finof the propulsion system using different angle of attack profiles.

DETAILED DESCRIPTION

Various exemplary embodiments and details are described hereinafter,with reference to the figures when relevant. It should be noted that thefigures may or may not be drawn to scale and that elements of similarstructures or functions are represented by like reference numeralsthroughout the figures. It should also be noted that the figures areonly intended to facilitate the description of the embodiments. They arenot intended as an exhaustive description of the disclosure or as alimitation on the scope of the disclosure. In addition, an illustratedembodiment needs not have all the aspects or advantages shown. An aspector an advantage described in conjunction with a particular embodiment isnot necessarily limited to that embodiment and can be practiced in anyother embodiments even if not so illustrated, or if not so explicitlydescribed.

The figures are schematic and simplified for clarity, and they merelyshow details which aid understanding the disclosure, while other detailshave been left out. Throughout, the same reference numerals are used foridentical or corresponding parts.

A propulsion unit for propelling a vessel is disclosed. The propulsionunit comprises a main body configured to be arranged at a keel of thevessel and comprising a pivot point (such as a first pivot point), a finbeing movably arranged in relation to the main body, and an actuatorassembly for generating a heave motion of the fin in relation to themain body. The heave motion may herein refer to a reciprocating motionof the fin, such as a linear vertical upwards/downwards motion of thefin in relation to the main body, when the propulsion unit is arrangedon the vessel. The actuator assembly comprises at least one actuator.The fin is connected to the pivot point such that the fin is arranged topivot around the pivot point when the at least one actuator generatesthe heave motion of the fin, thereby generating a pitch motion of thefin. The pitch motion of the fin herein refers to a rotation of the finabout its transverse axis, such as an axis extending from a first tip ofthe fin to a second tip of the fin, such as port side tip of the fin toa starboard side tip of the fin). The heave motion and/or pitch motionof the fin generates a thrust force for propelling the vessel.

The at least one actuator may be a linear actuator. The actuator may bea hydraulic, electric or mechanic actuator. The actuator may in one ormore example propulsion units be a ram style actuator. The propulsionunit may comprise at least one actuating rod. The actuator assembly maybe connected to the fin via the at least one actuating rod. The actuatorassembly may be configured to operate with an oscillating pattern,thereby generating an oscillating heave and pitch motion of the fin.

In one or more example embodiments of the propulsion unit, the pivotpoint may be fixedly arranged to the main body. The propulsion unit maycomprise a lever arm. The lever arm may be attached to the pivot point,such that the lever arm may pivot around the pivot point. The fin may beattached to the pivot point via the lever arm. Since the fin may beattached to the lever arm being pivotably attached to the pivot point,the fin may pivot around the pivot point.

In one or more example embodiments of the propulsion unit, the fin maybe pivotably arranged to the lever arm. The propulsion unit may furthercomprise a pitch rod configured to change the pitch of the fin when theactuator generates the heave motion of the fin. A first end of the pitchrod may be pivotably arranged to the fin at a distance from the pivotpoint at which the fin is attached to the lever arm. The propulsion unitmay comprise a crank, such as a bell crank, having a first and a secondarm and being pivotably arranged to the main body of the propulsion unitat a distance from an end of the first and second arm, respectively. Asecond end of the pitch rod may be pivotably arranged on a first end ofthe crank and the actuator may be pivotably arranged to the second endof the crank. Upon the actuator performing a reciprocating motion, thecrank may rotate around the pivot point thereby changing the position ofthe second arm of the crank which changes the position of the second endof the pitch rod. This causes the first end of the pitch rod to changethe position in relation to the pivot point joining the fin to the leverarm which leads to the fin changing the pitch angle relative to thelever arm. The crank may further comprise a first contacting surface anda second contacting surface facing each other and being configured tocontact an upper side and a lower side of the lever arm, respectively,to generate the heave motion of the fin. Upon extension of the actuator,the crank may pivot in relation to the main body, so that the firstcontacting surface of the crank contacts the upper side of the lever armand pushes the lever arm downwards. Upon retraction of the actuator, thecrank may pivot in an opposite direction relative to the main body, sothat the second contacting surface of the crank contacts the lower sideof the lever arm and pushes the lever arm upwards.

In some example embodiments, the pitching motion of the fin may also begenerated by the actuator being a rotating actuator. In some exampleembodiments of the propulsion unit, the actuator assembly may comprise afirst actuator and a second actuator. The first actuator and the secondactuator may be connected to the fin via a first pivot point andoptionally a second pivot point, respectively. The pivot point, such asthe first pivot point and/or the second pivot point, may thus be movablyarranged in relation to the main body. The positions of the pivot pointsand/or the actuators connected to them may be moved forward or aft onthe fin body, so that they are placed in order to optimize their inducedtorque on the fin.

The first actuator and the second actuator may be independently operablein relation to each other, so that a phase difference between the heavemotion and the pitch motion of the fin is variable. The first actuatorand the second actuator may thus be operated in phase or out of phase.In order to create a pitch and heave motion which is out of phase, theactuators may be operated with a phase difference. Varying the phasedifference allows an adjustment of the maximum angle of pitch of thefin. The two actuators may in one or more embodiments be operated byindependently varying the amplitude of their travel or motion. The firstactuator and the second actuator may thus vary the amplitude and/or thephase of their travel or motion independently of each other. The angleof pitch herein is an angle of the fin to a horizontal plane. When thefirst actuator and the second actuator are operated in phase, the finonly performs a heave motion since the relative position of the firstand second pivot points does not change. In other words, when the firstand the second actuators are operated in phase, they perform the samemovement, the pitch of the fin is thus not changed, and the fin performsthe upward/downward motion without changing the angle of the fin to thehorizontal plane. When the first actuator and the second actuator areoperated out of phase, the fin performs a heave motion and a pitchmotion since the relative position of the first and second pivot pointschanges. In other words, when the first and the second actuators areoperated out of phase, they perform the different movements, the pitchof the fin is thus changed, and the fin performs the upward/downwardmotion while changing the angle of the fin to the horizontal plane.Since the first actuator and the second actuator may be independentlyoperable, a motion pattern of the fin may be adapted and optimized toincrease the lift of the fin, and thus the thrust force generated by thefin. By significantly changing and/or reversing the phase or amplitudeof the first actuator and/or the second actuator the fin may produce areverse thrust for reversing the vessel. By controlling the phasedifference and/or the amplitude of the of the first actuator and thesecond actuator individually, a precise control of the motion of the finmay be achieved. Thus, the one or more example embodiments disclosedherein provide a simple system which allows a precise control of themotion of the fin.

In one or more example embodiments of the propulsion unit, the fin maybe slidably arranged inside of the main body. The fin may comprise afirst fin section, a second fin section and a connecting element forconnecting the first fin section and the second fin section. Theconnecting element may comprise a first connecting rod and optionally asecond connecting rod. The first fin section and the second fin sectionmay be connected via the first connecting rod and the second connectingrod. The first connecting rod and the second connecting rod may bearranged in parallel and at a respective first distance and seconddistance from a leading edge of the first and second fin sections. Thefirst and second connecting rods may have a respective first and secondend section configured to be arranged inside the first and the secondfin section, respectively. A center section of the first connecting rodand the second connecting rod may be arranged inside the main body. Thefirst fin section and the second fin section may be arranged on oppositesides of the main body, such that the main body separates the first finsection and the second fin section. The first fin section may thus bearranged on a first side, such as on a starboard side, of the main bodyand the second fin section may be arranged on a second side, such as ona port side, of the main body.

The first connecting rod may be connected to the first actuator and thesecond connecting rod may be connected to the second actuator. The firstconnecting rod and the second connecting rod may be connected to therespective first actuator and second actuator via a first actuating rodand a second actuating rod, respectively. The first connecting rod maybe connected to the first actuating rod via a first freely rotatingpinned connection. The second connecting rod may be connected to thesecond actuating rod via a second freely rotating pinned connection. Thefirst freely rotating pinned connection may thus constitute the firstpivot point and optionally the second freely rotating pinned connectionmay constitute the second pivot point around which the fin is arrangedto pivot.

The at least one actuator may comprise one or more pinned connection atits ends for connecting the actuator to the fin, the actuating rodand/or the hull of the vessel. The at least one actuating rod may alsocomprise one or more pinned connections at its ends for connecting theactuator rod to the actuator and/or to the fin. The pinned connectionallows the actuator to rotate freely at the connecting points and thusallows the actuator to adjust its alignment to the lever arm and/or thevessel during the pivotal movement of the fin around the pivot point.The at least one actuator comprising the pinned connection can thus notcarry any bending moment.

The at least one actuator and/or the at least one actuating rod may inone or more example embodiments be restrained, e.g. by one or morebearings, such as sliding bearings, to only move in a longitudinaldirection, such as in the direction of the linear actuation of the atleast one actuator, so that it cannot rotate and can thus support abending moment in the actuator. The at least one actuator and/or the atleast one actuating rod, such as at least one of the first and thesecond actuator, may be restrained such that it can only be displaced ina vertical direction. The vertical direction may correspond to avertical direction of the vessel when the propulsion unit is arranged onthe vessel. Only being displaced in a vertical direction may herein beseen as the displacement of the actuator not having a component ineither longitudinal or lateral direction of the vessel. The at least oneof the first actuator and the second actuator may be configured to bedisplaced in a vertical direction. The at least one of the firstactuator and the second actuator may be restrained in a lateral and/orlongitudinal direction. The at least one actuator may be restrained suchthat it cannot pivot in relation to the vessel, such as in relation tothe hull of the vessel. The at least one actuator, such as at least oneof the first actuator and the second actuator may restrained in adirection perpendicular to a direction of extension of the at least oneactuator, such as in a direction perpendicular to a direction ofextension of at least one of the first actuator and the second actuator.

The one or more bearings may be arranged in the main body of thepropulsion unit and/or in the hull of the vessel. The one or morebearings may be arranged around a circumference of the at least oneactuator and/or the at least one actuating rod. The one or more bearingsmay be configured to support forces acting on the at least one actuatorand/or the at least one actuating rod in a direction perpendicular tothe direction of the linear actuation of the at least one actuator, suchas in a vertical direction when the propulsion unit is mounted to thevessel. Restricting the movement of the at least one actuator and/or theat least one actuating rod to a longitudinal direction facilitates asealing of the at least one actuator and/or the at least one actuatingrod to the vessel. Since the at least one actuator and/or the at leastone actuating rod cannot rotate in relation to each other, and/or inrelation to the hull of the vessel, simpler and less costly seals may beused than compared to solutions where the at least one actuator and/orthe at least one actuating rod can rotate in relation to vessel.Restraining the movement of the at least one actuator and/or actuatingrod improves the controllability of the movement of the fin and allowsthe motion of the fin to be controlled precisely. Restraining themovement of the at least one actuator and/or actuating rod prevents thefin from oscillating fore and aft during the heave and/or the pitchmotion of the fin in relation to the hull of the vessel.

In one or more example propulsion units, the propulsion unit comprises aplurality of actuators and/or actuating rods, such as for example afirst actuator and/or actuating rod, a second actuator and/or actuatingrod and a third actuator and/or actuating rod. One of the plurality ofactuators and/or actuating rods may be restrained, such that theactuator and/or actuating rod is prevented from rotating relative to thehull of the vessel. The other actuators and/or actuating rods of theplurality of actuators and/or actuating rods may be configured to pivotin relation to the hull of the vessel while performing the heave and/orthe pitch motion of the fin. The fin may be configured to pivot inrelation to each one of the plurality of actuators and/or actuatingrods, such that the fin can change its angle of attack in relation toeach of the plurality of actuators and/or actuating rods. The fin mayfor example be connected to the plurality of actuators and/or actuatingrods via a respective pivot point.

When the fin performs a pitch motion, the distance between the firstpivot point and the second pivot point, seen from a horizontal plane,such as a plane perpendicular to the longitudinal extension of theactuating rods, varies. In order to allow for a change in the distancebetween the first pivot point and the second pivot point, seen from thehorizontal plane, at least one of the pivot points may be connected tothe fin via a sliding joint. The sliding joint may e.g. be an elongatedslot in which the pivot point may be arranged to slidably move.

At least one of the first and second connecting rods, such as the firstconnecting rod, may comprise a first and a second elongated slotarranged at opposite ends of the connecting rod, respectively. Theelongated slots may have a longitudinal extension in a directionperpendicular to a longitudinal axis of the at least one of the firstand second connecting rods. The elongated slots may be arranged insidethe first and second fin section, respectively. The first elongated slotand the second elongated slot may be connected to a pin or a rod fixedlyarranged inside the first fin section and the second fin section,respectively, such that the pin or rod is slidably arranged within theelongated slot of the at least one of the first and second connectingrods. The first and the second fin sections may also comprise anelongated slot for receiving the first connecting rod and/or the secondconnecting rod, thereby allowing the first connecting rod and/or thesecond connecting rod to slide inside the elongated slot relative to thefirst and the second fin section. The first connecting rod and/or thesecond connecting rod may thus be slidably arranged inside the first andthe second fin sections in a direction perpendicular to the longitudinalaxis of the at least one of the first and second connecting rods, suchthat the distance of the first connecting rod and/or the secondconnecting rod from the leading edge can be varied. By varying thedistance of the first connecting rod and/or the second connecting rodfrom the leading edge, the distance between the first pivot point andthe second pivot point, seen from the horizontal plane, may change withthe pitch motion of the fin. Thereby, the first actuator and the secondactuator may perform a purely vertical motion for generating both thepitch and the heave motion of the fin. The location of the firstconnecting rod and the second connecting rod, and thus the location ofthe connection points to the first and second actuators, may be up toimplementation and may be moved along the chord of the fin body, so thatthe connection points to the first and second actuators, are placed inorder to optimized the torque induced onto the fin.

The first actuating rod and/or the second actuating rod (or at leastcenter sections thereof) may be arranged inside the main body. Thus, themain body may comprise a first through-going slot and/or a secondthrough-going slot for receiving the first connecting rod and/or thesecond connecting rod respectively. The first through-going slot and/orthe second through-going slot allows the first connecting rod and thesecond connecting rod to protrude through the main body and to beslidably arranged within the first through-going slot and the secondthrough-going slot. The first connecting rod and the second connectingrod may connect to the first actuating rod and the second connecting rodinside the main body. The first through-going slot and the secondthrough-going slot have a longitudinal extension in a vertical directionof the main body, to allow the first connecting rod and the secondconnecting rod to perform a vertical movement to generate the pitch andthe heave motion of the fin. The first through-going slot and the secondthrough-going slot may comprise an opening at a top end of the firstthrough-going slot and the second through-going slot, respectively. Theopenings at the top end of first through-going slot and the secondthrough-going slot, allow the first and second actuators and/or firstactuating rod and the second actuating rods to protrude into main bodyto connect to the connecting rods. The openings at the top end of firstthrough-going slot and the second through-going slot may extend upwardsinto the main body and/or hull of the vessel and may be sealed above thewaterline of the vessel.

The propulsion unit may comprise a rudder. In one or more exampleembodiments, the main body may be configured to be fixedly arranged tothe keel of the vessel, and the rudder may be pivotably arranged to theskeg. When the main body is fixedly arranged to the keel it mayconstitute a skeg of the vessel. Skeg herein means a sternward extensionof the keel of the vessel. The skeg may provide directional stability tothe vessel. The main body may have a rudder mounted on its center line.The rudder may be attached to the main body via a rudder stock arrangedat a trailing edge of the main body. The rudder stock is a verticalshaft through which the turning force of the steering gear may betransmitted to the rudder. The rudder stock may thus provide the pivotpoint for the rudder, around which the rudder may be pivotably arrangedto the main body.

In one or more example embodiments, the main body may comprise a rudderstock for rotatably arranging the main body to the keel of the vessel.The main body may thus be configured to rotate and act as the rudder.The rudder stock may be hollow to accommodate the one or more actuatorsand/or the at least one actuating rod. The one or more actuators and/orthe at least one actuating rod may be arranged inside the rudder stock.The rudder stock may comprise a bearing, such as a rotating bearing, forrotatably arranging the rudder stock to the keel of the vessel. Therudder stock may constitute a bearing race of the bearing. In order toprevent water from entering the vessel through the hollow rudder stock,the rudder stock may be sealed. The rudder stock constituting one of thebearing races may be extended above the waterline of the vessel, suchthat the rudder stock may be sealed above the waterline. Sealing therudder stock above the waterline allows simpler and less expensive sealsto be used compared to when the rudder stock is sealed below thewaterline of the vessel.

The main body may comprise a hollow tube protruding from the main bodyon a vessel- or keel-facing side of the main body. The first actuatingrod and/or the second actuating rod may be arranged within the hollowtube. The hollow tube may be configured to protrude into the vessel,such as into the inside of a hull of the vessel, when the main body isarranged to the keel of the vessel. When the main body is fixedlyarranged to the keel of the vessel, the hollow tube may be a steel tubewelded to the hull of the vessel. When the main body is rotatablyarranged to the keel of the vessel, the rudder stock may be hollow andmay constitute the hollow tube. The hollow tube may comprise a first endarranged to protrude into the hull of the vessel and a second endarranged in and/or at the main body of the vessel. The first end of thehollow tube is thus located further away from the main body and/or thefin than the second end of the hollow tube. Thus, the first end of thehollow tube may herein be referred to as a distal end of the hollowtube. The main body may be wholly or partially open to the watersurrounding the vessel. In order to allow a movement of the actuators,actuator rods and/or connecting rods inside the main body, the main bodycomprises openings, such as slots, for receiving the actuators, actuatorrods and/or connecting rods. Water may thus protrude through theopenings in the main body. In order to prevent water to enter into thehull of the vessel, the hollow tube may comprise a seal arranged at thefirst end, such as the distal end, of the hollow tube, for sealing theactuators and/or the actuator rods to the hollow tube. The hollow tubemay comprise a flanged connection for receiving the seal. Sealingbetween the actuators and the hull shell, may be particularlycomplicated and difficult if the seal is arranged below a waterline ofthe vessel. By providing the hollow tubes on the main body, thatprotrude into the hull of the vessel, and arranging the seal at thefirst end, such as the distal end, of the hollow tube inside the hull ofthe vessel, the seal may be moved upwards, such that the connectionbetween the actuators and the hull of the vessel and/or between theactuating rods and the hull of the vessel can be arranged above thewaterline of the vessel. Thereby the connection between the actuatorsand the hull of the vessel and/or between the actuating rods and thehull of the vessel may be sealed using less complicated and lessexpensive seals. The first actuator and/or the second actuator may besealed internally to prevent water from entering the vessel through theactuator.

In one or more example propulsion units, the first actuator and thesecond actuator and/or the first actuating rod and the second actuatingrod may be arranged in the same hollow tube. In one or more exampleembodiments of the propulsion unit, such as e.g. when the main body isfixedly arranged on the keel of the vessel, the main body may comprise afirst and a second hollow tube. The first actuator and the secondactuator and/or the first actuating rod and the second actuating rod maybe arranged in a respective hollow tube. The first actuator and/or thefirst actuating rod may be arranged within the first hollow tube and thesecond actuator and/or the second actuating rod may be arranged withinthe second hollow tube.

In one or more example propulsion units, the propulsion unit, such asthe actuator assembly, comprises a third actuator, such that thepropulsion unit comprises at least three actuators. The at least threeactuators may be arranged between the hull of the vessel and the fin.The at least three actuators are configured to provide the heave andpitch motion of the fin in relation to the hull of the vessel. At leastone of the three actuators may be configured to only perform a movementin a vertical direction of the main body. The other actuators may beconfigured to perform a movement in a vertical and in a longitudinaldirection of the main body. The at least one actuator being configuredto only perform a movement in the vertical direction may be restrainedin its movement by a support. The support may prevent the at least oneactuator and/or the at least one actuating rod being configured to onlyperform the vertical movement to move in any other direction than thevertical direction.

In one or more example propulsion units, at least two of the firstactuator, the second actuator and the third actuator may becorrelatively operable, such as operable simultaneously and relative toeach other, to variably adjust the pitch angle and/or the heave of thefin. For example, in order to change the pitch of the fin, two of thethree actuators may be operated simultaneously and relative to eachother, such as being retracted or extended relative to each other, tochange the vertical distance between the respective pivot points towhich the two actuators are connected. One of the actuators may not bedisplaced, such that the fin can pivot around the pivot point connectingthe actuator not being displaced to the fin. In order to perform a heavemotion of the fin, all three of the actuators may be operatedsimultaneously

In order to control the heave and the pitch motion of the fin, the firstactuator, the second actuator and the third actuator may be individuallycontrolled. The first actuator, the second actuator and the thirdactuator may be connected to the main body of the propulsion unit (or tothe hull of the vessel) and/or to the fin via respective pivot points.The pivot points of the fin may be arranged at respective distances fromthe leading edge of the fin, such that the first, the second and thethird actuators are acting on the fin at respective distances from theleading edge of the fin. For example, the first actuator may be arrangedcloser to a leading edge of the fin than the second actuator and thethird actuator. The second actuator may be arranged closer to theleading edge of the fin than the third actuator but farther from theleading edge than the first actuator. The third actuator may be arrangedfarther from the leading edge than both the first actuator and thesecond actuator.

The third actuator may be of the same type as the first and secondactuators or of a different type than the first and the secondactuators. The third actuator may in one or more example propulsionunits be a hydraulic ram-type actuator. The third actuator may be anactuating rod. The third actuator may be connected to the fin at adistance from the first and the second actuators in a longitudinaldirection, such as in a fore/aft direction, of the vessel. The firstactuator, the second actuator and/or the third actuator may be connectedto the fin and/or to the hull of the vessel via one or more fixed pivotpoints. Fixed pivot point herein means that the pivot point is fixedly,such as not slidably, arranged, to the fin, to the hull of the vesseland/or to the main body of the propulsion unit. The pivot points may inone or more example propulsion units be pinned joints that are fixed tothe fin and/or to the main body of the propulsion unit and/or to thehull of the vessel. By fixedly arranging the first and the second pivotpoints in the fin, the stability and/or controllability of the fin maybe increased, such that the pitch of the fin may be controlled with anincreased precision. Furthermore, by not having a sliding joint, such asa slidably arranged pivot point, in the fin, the friction induced intothe system may be reduced thereby increasing the efficiency of thepropulsion unit. Reducing the movable parts of the propulsion unit beingarranged under water, further reduces the risk of corrosion andpotential seizing of the moving parts and a potential malfunction of thesystem. Thereby, the performance of the propulsion unit may be improved.

The displacements, such as the respective displacement, of theactuators, such as the first actuator, the second actuator and/or thethird actuator, may for example be controlled such that one of theactuators only performs a vertical displacement with no motion componentin a fore and/or aft direction, such as in the longitudinal direction,of the vessel. By restraining the movement of one of the threeactuators, the motion of the fin can be controlled in a more precisemanner. For example, the fin can be prevented from oscillating in afore/aft direction of the vessel while performing the heave and/or pitchmotion, which improves the efficiency of the propulsion unit since anoscillation of the fin in a fore/aft direction may change the pitchangle of the fin.

The displacement of the actuators may be controlled to adjust the heaveand pitch based on conditions of the water surrounding the fin, such asbased on an incoming water velocity, such as a velocity of the watermeeting the leading edge of the fin. Thereby, the motion of the fin maybe adapted to increase the performance of the propulsion unit based onthe current conditions of the water surrounding the fin. The actuatorsmay for example be controlled based on a plurality of angle of attackprofiles depending on the conditions of the water. For example, a firstexample angle of attack profile may be optimized for open water. Asecond example angle of attack profile may be optimized for operation ina wake behind the vessel. The propulsion unit according to the currentdisclosure, such as the propulsion unit comprising two or moreactuators, can continuously adapt the heave and/or the pitch of the finand can thus adjust the motion of the fin to more or less an infinitenumber of angle of attack profiles. The plurality of angle of attackprofiles may for example be determined using Computational FluidDynamics (CFD) codes with optimization routines in order to optimize amovement pattern and/or fin geometry based on a given water condition,such as a given inflow of water to the fin.

In one or more example propulsion units, the propulsion unit maycomprise a control system configured to optimize and control themovement pattern, such as the displacement, of the actuators fordifferent angle of attack profiles based on a detected angle of attackof the fin. The control system may, in one or more example propulsionunits, control the movement pattern in real time, for example by usingmachine learning. The control system may receive information about theconditions of the fin, such as a water flow around the fin, informationabout the pitch and/or the heave of the fin, such as a pitch angle, aheave and/or a velocity of the motion of the fin, such as a velocity ofthe pitch and/or the heave. The control system may use the receivedinformation to optimize the pitch and/or the heave motion of the fin toimprove the efficiency of the propulsion unit.

In one or more example propulsion units, at least one of the actuatorsmay be offset transversely from one or more other actuators, in order toabsorb twisting moments on the fin, that may for example be induced bywaves. Transversely herein means along the transverse axis of the fin,such as along an axis extending from a starboard side of the vessel to aport side of the vessel. Thereby, the performance of the fin may befurther increased. The at least one of the actuators may, in one or moreexample propulsion units, be offset from the one or more other actuatorsby a distance in the range of 50-500 mm, such as in a range of 100-200mm.

In one or more example propulsion units, such as when the propulsionunit comprises a third actuator, the fin may comprise a third connectingrod. The third actuator may be pivotably connected to the thirdconnecting rod. The third connecting rod may be connected to the thirdactuator via a third actuating rod. The third actuating rod may bearranged inside the main body of the propulsion unit. The first finsection and the second fin section may be connected via the thirdconnecting rod. The first connecting rod, the second connecting rod andthe third connecting rod may be arranged in parallel and at a respectivefirst distance, second distance and third distance from the leading edgeof the first and second fin sections.

In one or more example propulsion units, the main body may comprise athird through-going slot for allowing the third connecting rod toprotrude through the main body and to be slidably arranged within thethird through-going slot.

The fin may have an elliptical planform. In some embodiments, such as inone or more example propulsion units, the fin may have a high aspectratio elliptical planform. The aspect ratio of the fin is the ratio ofthe its span to its mean chord. The span of the fin is the distance fromone fin tip to the other fin tip. The chord is an imaginary straightline joining the leading edge and the trailing edge of the fin. Theaspect ratio is equal to the square of the wingspan divided by the wingarea. Thus, a long, narrow fin has a high aspect ratio, whereas a short,wide fin has a low aspect ratio. A lift-to-drag ratio of the finincreases with the aspect ratio, hence having a high aspect ratio finimproves the performance and efficiency of the fin, which may improvefuel economy of the vessel. The lift-to-drag ratio, which may also bereferred to as L/D ratio, is the amount of lift generated by the fin,divided by the hydrodynamic drag it creates by moving through a viscousfluid, such as water. The chord shape and/or the planform shape of thefin may be altered, e.g. based on the shape of the hull of the vessel,to reduce drag of the fin.

The fin may comprise winglets. The winglets are endplates arranged onthe tip of the fin, which may extend in a direction perpendicular, or atleast substantially perpendicular, to a main plane of the fin. Thewinglets may improve the efficiency of the fin by reducing thehydrodynamic drag of the fin. The drag of the fin may be reduced bypartial recovery of the tip vortex energy. The winglets smoothen thewater flow across the fin near the tip which may increase the liftgenerated at the tip of the fin, which reduces a lift-induced dragcaused by vortices around the tip of the fin. Reducing the lift-induceddrag improves a lift-to-drag ratio of the fin. This increases efficiencyof the fin. The winglets may also increase efficiency of the fin byreducing vortex interference with a laminar flow of water near the tipsof the fin, by moving the confluence of low-pressure and high-pressureareas of water away from the surface of the fin. Vortices around the tipof the fin may create turbulence, originating at the leading edge of thefin tip and propagating backwards and inboard the fin. This turbulencemay delaminate the flow of water over a small triangular section of theoutboard fin, which may destroy the lift created by the fin in thatarea. The winglets move the area where the vortex forms away from thefin surface, since the center of the resulting vortex is now at the tipof the winglet. Since the fin performs an upwards/downwards motion,which may also be referred to an up/down stroke, during operation of thepropulsion unit, winglets may be arranged on both an upper and a lowerside of the fin. Since the lift is reversable on the fin between the upand down stroke, arranging winglets on both the upper and the lower sideof the fin increases the efficiency of the fin on both the up and thedown stroke.

The stroke of the fin, such as the displacement of the heave motion, maybe dependent on the size of the vessel and/or the draught of the vessel.The larger the vessel and/or the deeper the draught of the vessel, thelarger the stroke may be. By increasing the stroke of the fin, theefficiency of the fin and thereby the propulsion unit may be increased.In one or more example propulsion units, the stroke may be in a range of3 to 20 meters, such as in a range of 5 to 15 meters.

Further, a vessel comprising the propulsion unit for propelling thevessel according to this disclosure is disclosed. The vessel comprises akeel. The main body of the propulsion unit may be arranged to the keelof the vessel. The fin is configured to perform a pitch and heave motionin relation to the keel of the vessel. In one or more exemplaryembodiments, the vessel may comprise a plurality of propulsion units,such as when the vessel comprises several engines.

In one or more example embodiments, the main body may be fixedlyarranged to the keel of the vessel. Thereby the main body is stronglyattached to the hull and the hydrodynamic drag of the main body isreduced.

In one or more example embodiments, the main body may be rotatablyarranged to the keel of the vessel. The main body and rudder parts maythereby be integrated into one unit and the whole unit made to turn likea rudder. This may improve the maneuverability of the vessel.

FIGS. 1A and 1B illustrate a propulsion unit 1 for propelling the vessel100 according to one or more first example embodiments herein. In theone or more example embodiments shown herein the propulsion unit 1comprises a single actuator for generating the heave and pitch motion.The actuator acts on a lever arm attached to a pivot point at a firstend and to the fin in the other end. The pitch motion of the fin isgenerated by the lever arm rotating around the pivot point when theactuator exerts a heaving motion on the lever arm.

FIG. 1A shows a side view of the one or more first exemplary embodimentsof the propulsion unit 1. The propulsion unit 1 comprises a main body 2configured to be arranged at a keel 101 of the vessel 100 and comprisinga pivot point 5 a, a fin 3 being movably arranged in relation to themain body 2, and an actuator assembly 4 for generating a heave motion ofthe fin 3 in relation to the main body 2, the actuator assembly 4comprising an actuator 4 a. The fin 3 is connected to the pivot point 5a via a lever arm 7 such that the fin 3 is arranged to pivot around thepivot point 5 a when the actuator 4 a generates the heave motion of thefin 3, thereby generating a pitch motion of the fin 3. In the one ormore first example embodiments herein, a first end of the lever arm 7 isconnected to the pivot point 5 a and a second end of the lever arm 7 isconnected to the fin 3. The pivot point 5 a is fixedly arranged to themain body 2. The pivot point 5 a may be a pinned rotation point. Thepivot point 5 a may be arranged inside the main body 2, such that leverarm 7 may be connected to the pivot point on the inside of the main body2. The main body 2 may thus comprise a slot 2 a open towards an aft endof the main body 2 for allowing the lever arm 7 to protrude through themain body 2 and to perform the heave and pitch motion in relation to themain body 2. Since the slot 2 a is open the slot 2 a is configured to bein contact with water surrounding the vessel 100 during operation.

The actuator assembly 4 comprises a single actuator 4 a, for generatingthe heave and pitch motion of the fin 3. The propulsion unit 1 and/orthe actuator assembly 4 may comprise an actuating rod 9. The actuator 4a may be connected to the lever arm 3 via the actuating rod 9. Theactuating rod 9 may be connected to the lever arm 7 at a distance fromthe pivot point 5 a. The actuator 4 a thus exerts a force on the leverarm 7 via the actuating rod 9 at a distance from the pivot point 5 a,which force causes a torque on the lever arm 7 around the pivot point 5a.

The actuator 4 a, which may also be referred to as a first actuator 4 a,may be a linear actuator performing a linear motion. The actuator 4 amay be arranged to perform a vertical (up/down) motion. Since the leverarm 7 is connected to the pivot point 5 a, the linear vertical motion ofthe actuator 4 a causes the lever arm 7 to rotate around the pivot point5 a. The rotation of the lever arm 7 around the pivot point 5 a causesthe fin 3, which is attached to an opposite end of the lever arm 7 thanthe pivot point 5 a, to rotate around the pivot point 5 a and thus toperform a heave and pitch motion in relation to the hull of the vessel100. Since the pitch of the fin 3 is generated by the pivoting motion ofthe lever arm 7 during the heaving motion of the fin 3, the pitch of thefin 3 is directly dependent on the heave of the fin 3. The pitch and theheave of the fin 3 are thus always in phase with each other. Theactuating rod 9 may be connected to the lever arm 7 via a second pivotpoint 5 b thus allowing the actuating rod 9 and the lever arm 7 torotate in relation to each other. This allows an angle between thelinear actuator 4 a and the lever arm 7 to vary during the heave andpitch motion of the lever arm 7 and the fin 3. When the actuating rod 9is connected to the lever arm 7 via a second pivot point 5 b, the pivotpoint 5 a may be referred to as a first pivot point 5 a.

The actuator 4 a may be configured to be operated with an oscillatingpattern, thereby generating an oscillating heave and pitch motion of thefin 3. The oscillating heave and pitch motion may comprise an upwardstroke and a downward stroke. The upward stroke refers to a motion wherethe actuator 4 a pulls the fin 3 towards the vessel 10. The downwardstroke refers to a motion where the actuator 4 a pushes the fin 3 awayfrom the vessel 10. In FIG. 1A the lever arm 7 and the fin 3 are shownin an upper position, such as at an end position of the upward stroke.

When the fin 3 performs the pitch motion the distance between the firstpivot point 5 a and the second pivot point 5 b, seen from a horizontalplane, such as a plane perpendicular to the longitudinal extension ofthe actuating rod 9, varies. In order to allow for a change in thedistance between the first pivot point 5 a and the second pivot point 5b, seen from the horizontal plane, the second pivot point 5 b may beconnected to the lever arm 7 via a sliding joint 7 a. The sliding joint7 a may e.g. be an elongated slot in which the second pivot point 5 bmay be arranged to slidably move. The second pivot point 5 b may thus bemovably arranged in relation to the fin 3.

The fin 3 comprise winglets 15. The winglets 15 are endplates arrangedon the tip of the fin 3, and extending in a direction perpendicular, orat least substantially perpendicular, to a main plane of the fin 3. Thewinglets 15 improve the efficiency of the fin 3 by reducing thehydrodynamic drag of the fin 3. Winglets 15 may be provided on a topand/or a bottom side of the fin 3. In the one or more embodiments shownherein, winglets 15 are provided on both the top and the bottom side ofthe fin 3. Thereby, the efficiency of the fin 3 is improved on both theupward stroke and the downward stroke of the fin 3.

The propulsion unit 1 may further comprise a rudder 6. The main body 2may be rotatably arranged to the vessel 100, such that the main body 2may act as a rudder 6. The fin 3 is thus arranged to rotate togetherwith the rudder 6. The main body 2 may be arranged to the vessel via arudder stock. The rudder stock may be hollow to accommodate the actuator4 a and/or the actuating rod 9. The actuator 4 a and/or the actuatingrod 9 may thus connect to the lever arm 7 through the hollow rudderstock. The rudder stock may be rotatably arranged to the vessel 100 viaa bearing, such as a rotating bearing. The rudder stock may constitute abearing race of the bearing. In order to prevent water from entering thevessel through the hollow rudder stock, the rudder stock may have to besealed. The rudder stock constituting one of the bearing races may beextended above the waterline of the vessel 100, such that the rudderstock may be sealed above the waterline. Sealing the rudder stock abovethe waterline allows simpler and less expensive seals to be usedcompared to when the rudder stock is sealed below the waterline. Thepropulsion unit 1 may however also be fixedly arranged to the vessel100. When the propulsion unit 1 is fixed to the vessel 100, the vessel100 may comprise a traditional rudder 6 arranged behind the fin 3.

FIG. 1B shows a perspective view of the propulsion unit 1 for propellingthe vessel 100, according to one or more example embodiments shown inFIG. 1A. As can be seen the main body 2 is arranged on the keel 101 ofthe vessel 100. The lever arm 7 is pivotably connected to the main body2 via the pivot point 5 a (not shown in FIG. 1B) arranged inside themain body 2. A second end of the lever arm 7 is connected to the fin 3.The main body 2 comprises the slot 2 a open towards an aft end of themain body 2 for allowing the lever arm 7 to perform a vertical motion inrelation to the main body 2. The lever arm 7 is connected to theactuator 4 a (not shown in FIG. 1B) via the actuating rod 9. Theactuating rod 9 may perform a linear vertical motion, such as an up/downmotion, which motion is transferred to the fin 3 via the lever arm 7. InFIG. 1B the lever arm 7 and the fin 3 are shown in an upper position,such as in an end position of an upward stroke.

The fin 3 has an elliptical planform, such as a high aspect ratioelliptical planform. The aspect ratio of the fin is the ratio of the itsspan s to its mean chord c. Thus, a fin having a high aspect ratioplanform means that the fin 3 is long and narrow. The lift-to-drag ratioof the fin increases with the aspect ratio, hence high aspect ratio fin3 disclosed herein improves the performance and efficiency of the fin 3,which may improve fuel economy of the vessel. The lift-to-drag ratio,which may also be referred to as L/D ratio, is the amount of liftgenerated by the fin, divided by the hydrodynamic drag it creates bymoving through a viscous fluid, such as water. The shape of the chord cand/or the planform shape of the fin 3 may be up to implementation andmay be altered, e.g. based on the shape of the hull of the vessel 100,to reduce the hydrodynamic drag of the fin 3.

As can be seen in FIG. 1B, according to the one or more firstembodiments of the propulsion unit 1 shown herein, winglets 15 areprovided on both the top and the bottom side of the fin 3 to improve theefficiency of the fin 3 on both the upward stroke and the downwardstroke.

The propulsion unit 1 according to the one or more first exampleembodiments herein has a simple layout comprising only one actuator forperforming the heave and the pitch motion and thus has a high mechanicalefficiency and low maintenance requirements.

FIG. 2A to 2D illustrate the propulsion unit 1 and a motion pattern ofthe propulsion unit 1 according to one or more second exampleembodiments herein. The actuator assembly 4 comprises the actuator 4 a,which may also be referred to as a first actuator 4 a, and a secondactuator 4 b. The pivot point 5 a (not shown in FIG. 2A to 2D) isconnected to the second actuator 4 b, such that the pivot point 5 a ismovably arranged in relation to the main body 2. The first actuator 4 aand the second actuator 4 b may be independently operable in relation toeach other, so that a phase difference between the heave motion and thepitch motion of the fin 3 is variable. The first actuator 4 a and thesecond actuator 4 b may be linear actuators. The pitch motion and theheave motion of the fin 3 may thus be controlled independently of eachother. The fin 3 is movably arranged to the main body 2. The fin 3comprises a first fin section 3 a and a second fin section 3 b, a firstconnecting rod 8 a (not shown in FIG. 2A to 2D) and a second connectingrod 8 b (not shown in FIG. 2A to 2D). The first fin section 3 a and thesecond fin section 3 b are connected via the first connecting rod 8 aand a second connecting rod 8 b. The first connecting rod 8 a and asecond connecting rod 8 b may form a structural element of the fin 3.The main body 2 comprises a first through-going slot 13 a and a secondthrough-going slot 13 b for receiving the first connecting rod 8 a andthe second connecting rod 8 b of the fin 3. The first through-going slot13 a and a second through-going slot 13 b allow the first connecting rod8 a and the second connecting rod 8 b to protrude through the main body2 in a lateral direction. The first connecting rod 8 a and the secondconnecting rod 8 b are slidably arranged within the first through-goingslot 13 a and the second through-going slot 13 b, respectively. Thefirst through-going slot 13 a and the second through-going slot 13 bhave a longitudinal extension in a lateral direction of the main body 2,thereby allowing the first connecting rod 8 a and the second connectingrod 8 b of the fin 3 to perform a vertical movement in relation to themain body 2, thereby allowing the fin 3 to perform a heave and pitchmotion in relation to the main body 2. The first actuator 4 a and thesecond actuator 4 b may be connected to the first connecting rod 8 a andthe second connecting rod 8 b, respectively. In order to accommodate theactuators 4 a and 4 b, the first through-going slot 13 a and the secondthrough-going slot 13 b may be open at a top end, such as an end of thefirst through-going slot 13 a and the second through-going slot 13 bfacing the vessel 100, when the propulsion unit 1 is arranged on thevessel 100. The actuators 4 a and 4 b may thus extend through the mainbody 2 in a vertical direction of the main body 2 and may connect to thefirst connecting rod 8 a and the second connecting rod 8 b protrudingthrough the main body 2 in a lateral direction of the main body 2.

The propulsion unit 1 disclosed herein, may further comprise a rudder 6.The main body 2 may be configured to be fixedly arranged to the vessel100, such as to the keel 101 of the vessel 100, and the rudder 6 may bepivotably arranged to the skeg 2. The rudder 6 may be mounted to acenter line of the main body 2. The rudder 6 may be attached to the mainbody 2 via a rudder stock arranged at a trailing edge of the main body2.

FIG. 2A shows the fin 3, such as the fin sections 3 a and 3 b, of thepropulsion unit 1 in a top position during an exemplary motion patternfor moving the fin 3. In this exemplary motion pattern, the firstactuator 4 a and the second actuator 4 b are operated with a phasedifference. The top position of the fin 3 corresponds to the top of thetravel of the fin 3, such as when the fin 3 reaches and end positionduring an upwards stroke. In this position the first and the secondactuators are both in an upper position and the fin sections 3 a and 3 bare horizontally arranged, such as having a pitch angle of 0°.

FIG. 2B shows the fin 3 of the propulsion unit 1 during a downwardstroke of the fin 3. Both the first actuator 4 a and the second actuator4 b are moving downward, thereby applying a downward heave motion to thefin 3. However, the second actuator 4 b has started the downward strokebefore the first actuator 4 a started the downward stroke. This causesthe leading edge 10 of the fin 3, such as the fin sections 3 a and 3 b,to move downward before the trailing edge 16 moves downward, whichcauses the fin 3 to have a pitch angle to a horizontal having a firstsign. The pitch angle may have a positive or a negative sign dependingon the definition of the coordinate system. In the example shown in FIG.2B and in FIG. 5 herein, this pitch angle, such as the pitch anglehaving the first sign, corresponds to a positive pitch angle.

FIG. 2C shows the fin 3 of the propulsion unit in a bottom positionduring the exemplary motion pattern for moving the fin 3. The bottomposition of the fin 3 corresponds to the bottom of the travel of the fin3, such as when the fin 3 reaches and end position during the downwardsstroke. In this position the first and the second actuators are both ina lower position and the fin sections 3 a and 3 b are horizontallyarranged, such as having a pitch angle of 0°.

FIG. 2D shows the fin 3 of the propulsion unit 1 during an upward strokeof the fin the exemplary motion pattern for moving the fin 3. Both thefirst actuator 4 a and the second actuator 4 b are moving upward,thereby applying an upward heave motion to the fin 3. Since the secondactuator 4 b started its downward stroke before the first actuator 4 astarted the downward stroke it, will also start the upward stroke beforethe first actuator 4 a. This causes the leading edge 10 of the fin 3,such as the fin sections 3 a and 3 b, to move upward before the trailingedge 16 moves upward, which causes which causes the fin 3 to have apitch angle to a horizontal having a second sign. In the example shownin FIG. 2D and in FIG. 5 herein, this pitch angle corresponds to anegative pitch angle.

FIG. 3 illustrates a connection for connecting the fin 3 to the firstactuator 4 a and the second actuator 4 b according to the one or moresecond example embodiments herein. The first connecting rod 8 a and thesecond connecting rod 8 b of the fin 3 are arranged in parallel and at arespective first distance and second distance from the leading edge 10of the first fin section 3 a and the second fin section 3 b of the fin3.

The first connecting rod 8 a is connected to the first actuator 4 a andthe second connecting rod 8 b is connected to the second actuator 4 b.The first connecting rod 8 a and the second connecting rod 8 b may beconnected to the respective first actuator 4 a and second actuator 4 bvia a first actuating rod 9 a and a second actuating rod 9 b,respectively. The first actuator 4 a and the second actuator 4 b may beconnected to the first connecting rod 8 a and the second connecting rod8 b via a first actuating rod 9 a and a second actuating rod 9 b,respectively, e.g. via a freely rotating pin connection. The firstactuating rod 9 a and a second actuating rod 9 b may e.g. comprise athrough-going hole at their respective lower end, through which thefirst connecting rod 8 a and the second connecting rod 8 b may beinserted respectively. A translational movement from the first actuator4 a and the second actuator 4 b may thus be transferred to the firstconnecting rod 8 a and the second connecting rod 8 b via the firstactuating rod 9 a and the second actuating rod 9 b, respectively.

The rotating pin connection however allows the allows the firstconnecting rod 8 a and the second connecting rod 8 b to rotate freelywithin the first actuating rod 9 a and the second actuating rod 9 b,respectively. The rotating pin connection between the actuating rods andthe connecting rods thereby constitute a respective pivot point. In theexample shown in FIG. 3 , the connection between the second actuatingrod 9 b and the second connecting rod 8 b constitutes the first pivotpoint 5 a and the connection between the first actuating rod 9 a and thefirst connecting rod 8 a constitutes the second pivot point 5 b. The fin3 may thus rotate in relation to the actuating rods 9 a, 9 b, in orderto change the pitch of the fin 3.

In order to compensate for a change in distance between the first andthe second connecting rods 8 a, 8 b, seen from a horizontal plane, whenthe fin 3 performs a pitch motion, one of the first connecting rod 8 aand the second connecting rod 8 b may be movably arranged within thefirst fin section 3 a and the second fin section 3 b. In one or moreexample embodiments, the second connecting rod 8 b is movably arrangedwithin the fin sections and may comprise a first and a second elongatedguide section 17 arranged at opposite ends of the connecting rod 8 b.The first and second elongated guide sections 17 may have a longitudinalextension in a direction perpendicular to a longitudinal axis of the atleast one of the first and second connecting rods. The first and secondelongated guide sections 17 may be configured to be arranged inside thefirst fin section 3 a and the second fin section 3 b, respectively. Thefirst and second elongated guide sections 17 may be configured to guidea first pin 18 fixedly arranged inside the first fin section 3 a and asecond pin 18 fixedly arranged inside the second fin section 3 b,respectively. The first and second elongated guide sections 17 may beelongated slots, elongated bearings or tracks being configured to guidethe first pin 18 and the second pin 18, respectively. The pin 18 maythus be slidably arranged within the elongated slot 17 of the secondconnecting rod 8 b.

In one or more example embodiments, the first and second pins 18 may beinstead be arranged on opposite ends of the one of the first connectingrod 8 a and the second connecting rod 8 b and the elongated guidesection may be arranged on the inside of the first fin section 3 a andthe second fin section 3 b. The second connecting rod 8 b may forexample comprise the first and the second pin 18 arranged at oppositeends of the connecting rod 8 b. The first and second elongated guidesections 17 arranged inside the first fin section 3 a and second finsection 3 b may have a longitudinal extension in a directionperpendicular to the span s of the first fin section 3 a and the secondfin section 3 b. The first pin 18 and the second pin 18 may be arrangedto slidably engage the first and second elongated guide sections 17fixedly arranged inside the first fin section 3 a and the second finsection 3 b, respectively. The first fin section 3 a and the second finsection 3 b may also comprise an elongated slot 19 for receiving thesecond connecting rod 8 b, thereby allowing the second connecting rod 8b to slide back and forth inside the elongated slot 19 in a directionperpendicular to the longitudinal axis of the second connecting rod 8 b,such that the distance between the second connecting rod 8 b and theleading edge 10 can be varied. This permits the actuating rod 9 b and/orthe actuator 4 b to perform a purely vertical motion, during a pitchmotion of the fin 3.

FIG. 4 shows the main body 2 comprising the first through-going slot 13a and the second through-going slot 13 b for receiving the firstconnecting rod 8 a and the second connecting rod 8 b of the fin 3. Thefirst connecting rod 8 a and the second connecting rod 8 b protrudethrough the main body 2 in a lateral direction. The first connecting rod8 a and the second connecting rod 8 b are slidably arranged within thefirst through-going slot 13 a and the second through-going slot 13 b,respectively. The first connecting rod 8 a and the second connecting rod8 b may also protrude through the through-going holes at the lower endof the first actuating rod 9 a and the second actuating rod 9 b,respectively The first through-going slot 13 a and the secondthrough-going slot 13 b have a longitudinal extension in a lateraldirection of the main body 2, thereby allowing the first connecting rod8 a and the second connecting rod 8 b to perform a vertical up/downmovement within the through-going slots 13 a and 13 b respectively. Thefirst through-going slot 13 a and the second through-going slot 13 b areopen at a top end, such as at an end facing the vessel 100, when thepropulsion unit 1 is arranged on the vessel 100, for allowing the firstactuating rod 9 a and the second actuating rod 9 b to enter thethrough-going slots 13 a, 13 b from a vertical direction. The open endsof the first through-going slot 13 a and the second through-going slot13 b may be joined to holes in the hull of the vessel above them toallow the actuating rods to travel vertically into the hull of thevessel 100 were the actuator assembly may be arranged.

FIG. 5 shows a graph illustrating an exemplary motion pattern of the fin3 when the first actuator 4 a and the second actuator 4 b are operatedwith a phase shift. The curve h2 shows the extension of the firstactuating rod 9 a from a position mid-stroke, such as a position in themiddle of the top of travel and the bottom of travel of the firstactuating rod. The curve h1 shows to the extension of the secondactuating rod 9 b from a position mid-stroke. The curve theta shows thecorresponding pitch angle of the fin in degrees to a horizontal. Inorder to create pitch and heave motion, which is out of phase, theactuators are operated with a phase difference. Varying this phasedifference allows an adjustment of the maximum angle of pitch of the fin3 during the heave motion. As can be seen in the graph, the secondactuating rod 9 b performs its motion slightly ahead of the secondactuating rod 9 a. As can be seen, the pitch angle of the fin is highestwhen the first and the second actuating rods 9 a and 9 b are mid-strokeand moving in the same direction, such as at t=0 during a downwardsstroke and at t=3 during an upwards stroke. When the first actuating rodand the second actuating rod are in the end positions, such as at thetop of travel or bottom of travel, such as at t_1.5 and t=4.5.

FIG. 6 discloses the propulsion unit 1 according to one or more thirdexemplary embodiments, in which the main body 2 is configured to berotatably arranged to the vessel 100. The propulsion unit 1 disclosedherein is similar to the propulsion unit 1 as disclosed in relation toFIGS. 2 a to 2D, FIG. 3 and FIG. 4 . The main body 2 comprises a rudderstock 11 for rotatably arranging the main body 2 to the keel 101 of thevessel 100. The rudder stock is arranged on a top side of the main body2, such as on a side facing a bottom of the vessel 100 when the mainbody 2 is mounted to the vessel 100. The main body 2 may thus beconfigured to rotate around the rudder stock 11 and act as the rudder 6.The rudder stock 11 may be hollow to accommodate the one or moreactuators 4 a, 4 b and/or the first actuating rod 9 a and/or the secondactuating rod 9 b. The one or more actuators 4 a, 4 b and/or the firstactuating rod 9 a and/or the second actuating rod 9 b may be arrangedinside the rudder stock 11, such that they can move vertically insidethe rudder stock 11. The rudder stock 11 may comprise a bearing, such asa rotating bearing, for rotatably arranging the rudder stock to thevessel 100, such as to the keel 101 of the vessel 100. In someembodiments, the rudder stock 11 may constitute a race of the bearing,such as an inner race of the bearing.

FIG. 7 discloses a vessel 100 comprising a propulsion unit 1 forpropelling the vessel 100 according to the one or more second exemplaryembodiments disclosed herein. The vessel 100 comprises a keel 101. Themain body 2 of the propulsion unit 1 may be arranged to the bottom ofthe vessel 100, such as to the keel 101 of the vessel 100. The fin 3 a,3 b is configured to perform a pitch and heave motion in relation to thebottom of the vessel 100, such as to the keel 101 of the vessel 100.When the fin 3, 3 a, 3 b performs the heave and pitch motion a thrustforce is generated for propelling the vessel 100. In the exemplaryembodiment shown in FIG. 7 , the propulsion unit 1 comprises twoactuators for generating the heave and pitch motion of the fin 3, 3 a, 3b. The motion pattern of the fin 3 may thus be precisely controlled tomatch the hull and the load of the fin 3 in a boundary layer of thehull. The main body 2 herein, is fixedly arranged to the vessel 100,such as to the keel 101 of the vessel 100, and may thus constitute askeg of the vessel 100. The propulsion unit further comprises a rudderattached to the trailing edge of the main body 2. However, the vessel100 may in one or more embodiment comprise a propulsion unit accordingto the one or more first and third exemplary embodiments disclosedherein.

FIG. 8 illustrates a perspective view of an inside of an exemplaryvessel 100 comprising an exemplary propulsion unit 1 according to thisdisclosure. The main body 2 is fixedly mounted to the vessel and thefirst actuator 4 a and the second actuator 4 b are arranged on theinside of the vessel 100. The propulsion unit 1 shown in FIG. 8comprises a sealing arrangement according to one or more exampleembodiments herein, for preventing water from entering into the vessel.In order for the first actuator 4 a and the second actuator 4 b togenerate the heave and pitch motion of the fin 3, 3 a, the hull and themain body comprises openings for receiving the first and the secondactuators 4 a, 4 b, and/or the first actuating rod and the secondactuating rods 9 a, 9 b. The openings are open to the water surroundingthe vessel 100. In order to prevent water from entering the vesselthrough the openings, the main body may comprise one or more hollowtubes 12; 12 a, 12 b protruding from the main body and into the vessel100. The first actuating rod 9 a and/or the second actuating rod 9 b andor the first actuator 4 a and/or the second actuator 4 b may be arrangedwithin the one or more hollow tubes 12; 12 a, 12 b. The one or morehollow tubes 12; 12 a, 12 b may be steel tube(s) welded to the hull ofthe vessel 100. The one or more hollow tube(s) 12; 12 a, 12 b maycomprise a first end, such as a distal end, arranged to protrude intothe hull of the vessel 100 and a proximal end arranged in the main body2 of the vessel 100. The first end, such as the distal end, of the oneor more hollow tube(s) 12; 12 a, 12 b may be configured to extend abovea waterline of the vessel 100. In order to prevent water to enter intothe hull of the vessel 100 through the openings, the one or more hollowtube(s) 12; 12 a, 12 b may comprise a seal 20 arranged at the distal endof the one or more hollow tube(s) 12; 12 a, 12 b, respectively. The oneor more hollow tube(s) 12; 12 a, 12 b may comprise a flanged connectionfor receiving the seal 20. By providing the one or more hollow tube(s)12; 12 a, 12 b on the main body 2, that protrude into the hull of thevessel 100, and arranging the seal 20 at a distal end of the one or morehollow tube(s) 12; 12 a, 12 b above the waterline of the vessel 100,less complicated and less expensive seals may be used.

FIG. 9 illustrates an example propulsion unit 1 according to the currentdisclosure. The example propulsion unit 1 comprises two actuators 4,such as the first actuator 4 a and the second actuator 4 b. One of thetwo actuators 4, such as the second actuator 4 b, is restrained in itsmovement, such that it can only be displaced, such as being extended orretracted, in a vertical direction, such as along a vertical axis, ofthe vessel. The example propulsion unit 1 comprises one or more supportsurfaces 21 for restraining the movement of the second actuator 4 b. Theone or more support surfaces may be roller supports and/or slidingbearings. The one or more support surfaces 21 may be fixedly arranged tothe hull of the vessel or to the main body of the propulsion unit 1. Theone or more support surfaces 21 may be configured to prevent the secondactuator 4 b from pivoting in relation to the hull of the vessel. Byrestraining the movement of the second actuator 4 b, the pivot point 5 bconnecting the second actuator 4 b to the fin 3 can only be displaced inthe vertical direction and can thus only perform a heave motion. The fin3 can however still pivot around the pivot point 5 b to allow a changeof the pitch of the fin 3. By restraining the movement of one of theactuators, such as the second actuator 4 b, the movement of the motionof the fin 3 can be precisely controlled. For example, the fin 3 can beprevented from oscillating in a fore/aft direction of the vessel whileperforming the heave and/or pitch motion. The first actuator 4 a may beunrestrained, such that it can pivot in relation to the hull of thevessel when the first actuator is being extended and/or retracted. Inone or more example propulsion units 1, the two actuators 4 a; 4 b maybe arranged at an angle to each other, such that a direction ofextension of the two actuators 4 a; 4 b are not parallel. For example,the first actuator 4 a may be arranged at an angle to the vertical axisof the vessel. The first pivot point 5 a and the second pivot point 5 bmay be fixedly arranged, such as not slidably arranged, in the fin 3. Inother words, the fin 3 can pivot around the first pivot point 5 a andthe second pivot point 5 b. The first pivot point 5 a and/or the secondpivot point 5 b may however not be slidably arranged in relation to thefin 3. The first pivot point 5 a and the second pivot point 5 b may inone or more example propulsion units be pinned joints. By fixedlyarranging the first and the second pivot points in the fin 3, thestability and/or controllability of the fin 3 may be increased, suchthat the pitch of the fin 3 may be controlled with an increasedprecision. Furthermore, by fixedly arranging the first and the secondpivot points 5 a, 5 b to the fin 3, the friction induced in thepropulsion system may be reduced, since there is no sliding movement inthe one or more connections between the actuators 4 a, 4 b and the fin3. Reducing the movable parts arranged under water of the propulsionunit 1, further reduces the risk of corrosion and potential seizing ofthe moving parts and a potential malfunction of the system. Thereby, theperformance of the propulsion unit may be improved.

FIG. 10 illustrates an example propulsion unit 1 according to thecurrent disclosure. The example propulsion unit 1 illustrated in FIG. 10comprises three actuators 4, such as the first actuator 4 a, the secondactuator 4 b and a third actuator 4 c. The first actuator 4 a, thesecond actuator 4 b and the third actuator 4 c may be connected to thefin via a respective pivot point, such as the first pivot point 5 a, thesecond pivot point 5 b and a third pivot point 5 c. In the examplepropulsion unit 1 disclosed in FIG. 10 , one of the three actuators 4,such as the second actuator 4 b, is configured to be displaced, such asbeing extended or retracted, in the vertical direction, such as alongthe vertical axis, of the vessel. The one of the three actuators 4, suchas the second actuator 4 b, may be restricted in the lateral and/or thelongitudinal direction, such that the one of the three actuators cannotbe displaced, such as being extended or retracted, in the lateral and/orthe longitudinal direction, such as along the lateral and/or thelongitudinal axis, of the vessel. Being configured to be displaced onlyin the vertical direction herein means that the second actuator does notmove in a fore and/or aft direction of the vessel when the actuator isextended and/or retracted. The restricted displacement of the secondactuator 4 b in the vertical direction only may be achieved bycontrolling an extension and/or retraction of each of the actuators 4 a,4 b, 4 c. By providing the propulsion unit 1 with a third actuator, themotion of the fin can be precisely controlled without using supportsurfaces for preventing the movement of the fin in a fore and/or aftdirection. By not using a support surface for controlling the motion ofthe fin, the friction between the support surface and the at least oneactuator may be reduced, thereby reducing the losses in the propulsionunit. Furthermore, by not having a support surface arranged under waterreduces the number of moving elements of the propulsion unit beingarranged underwater. Reducing the movable parts of the propulsion unitbeing arranged under water, further reduces the risk of corrosion andpotential seizing of the moving parts and a potential malfunction of thesystem. Thereby, the performance of the propulsion unit may be improved.

Due to the restraining of the movement of the second actuator 4 b, thepivot point 5 b connecting the second actuator 4 b to the fin 3 can onlybe displaced in the vertical direction and can thus only perform a heavemotion. The fin 3 is configured to pivot around the pivot point 5 b toallow a change of the pitch of the fin 3. By restraining the movement ofone of the three actuators, such as by restricting the movement of thesecond actuator 4 b, the motion of the fin 3 can be preciselycontrolled. For example, the fin 3 can be prevented from oscillating ina fore/aft direction of the vessel while performing the heave and/orpitch motion. The first actuator 4 a and/or the third actuator 4 c maybe unrestrained, such that they can pivot in relation to the hull of thevessel when the first actuator 4 a and/or the third actuator 4 c isbeing extended and/or retracted. In one or more example propulsion units1, the three actuators 4 a, 4 b, 4 c may be arranged at an angle to eachother, such that a direction of extension of the three actuators 4 a, 4b, 4 c are not parallel to each other. The actuators 4 a, 4 b, 4 c, suchas the ram-type actuators, may be arranged to the hull of the vessel sothat the actuators are arranged so that forces acting on the actuators 4a, 4 b, 4 c do not fight, such as work against, each other. One or moreof the actuators 4 a, 4 b, 4 c may be arranged such that the one or moreof the actuators 4 a, 4 b, 4 c are able to absorb forces in alongitudinal direction of the vessel and in a vertical direction of thevessel. The forces acting in a longitudinal direction may e.g. belongitudinal thrust forces. For example, the first actuator 4 a may bearranged at a first angle to the vertical axis of the vessel, the secondactuator 4 b may be arranged at a second angle, such as parallel, to thevertical axis of the vessel and the third actuator may be arranged at athird angle to the vertical axis of the vessel. The first pivot point 5a, the second pivot point 5 b and the third pivot point 5 c may befixedly arranged, such as not slidably arranged, to the fin 3. In otherwords, the fin 3 can pivot around the first pivot point 5 a, the secondpivot point 5 b and the third pivot point 5 c. By arranging two of theactuators, such as the first actuator 4 a and the third actuator 4 c atan angle different than zero to the vertical axis, the first actuator 4a and the third actuator 4 c can compensate for a change in distancebetween the first pivot point 5 a, the second pivot point 5 b and thethird pivot point, as seen from a horizontal plane, such as a planeperpendicular to vertical axis of the vessel, when the pitch angle ofthe fin 3 varies. The first pivot point 5 a, the second pivot point 5 band the third pivot point 5 c may in one or more example propulsionunits be pinned joints. By fixedly arranging the first pivot point 5 a,the second pivot point 5 b and the third pivot point 5 c in the fin 3,the stability and/or controllability of the fin 3 may be increased, suchthat the pitch of the fin 3 may be controlled with an increasedprecision.

In order to provide the pitch and/or heave motion of the fin 3, two ormore of the actuators 5 a, 5 b, 5 c may be operated in a correlatedmanner, such that the displacement of the actuators 5 a, 5 b, 5 c arecontrolled in a correlated manner. For example, in order to change thepitch of the fin 3, the first actuator 5 a may be extended while thethird actuator 5 c is retracted. This causes the fin 3 to pivot aroundthe second pivot point 5 b, such that the leading edge 10 of the fin 3is lowered and the trailing edge 16 of the fin 3 is raised. In order toraise the leading edge 10 and lower the trailing edge 16 of the fin 3,the first actuator 5 a may be retracted while the third actuator 5 c isextended. In order to change the heave of the fin 3, all of theactuators may be operated in a correlated manner. By retracting thefirst actuator 4 a, the second actuator 4 b and the third actuator 4 csimultaneously, the fin 3 may be lifted, such that the distance betweenthe fin 3 and the hull of the vessel decreases. By extending the firstactuator 4 a, the second actuator 4 b and the third actuator 4 csimultaneously the fin 3 may be lowered, such that the distance betweenthe fin 3 and the hull of the vessel increases. By independentlycontrolling the displacement, such as a rate of extension and/or a rateof retraction, of the first actuator 4 a, the second actuator 4 b andthe third actuator 4 c, a combined pitch and heave motion of the fin 3may be generated. This allows the heave and/or the pitch of the fin 3 ofthe propulsion unit 1 to be continuously adjusted to an infinite numberof angle of attack profiles. Thereby performance of the propulsion unit1 may be increased, as the angle of attack of the fin 3 towards theincoming water is a crucial factor for performance of the propulsionunit 1. The heave and/or pitch of the fin 3 may e.g. be controlled toincrease the efficiency of the fin 3 based on conditions of the watersurrounding the fin, such as based on an incoming water velocity, suchas a velocity of the water meeting the leading edge 10 of the fin 3. Thedisplacements of the actuators 5 a, 5 b, 5 c may for example becontrolled such that all forces acting on the actuators 5 a, 5 b, 5 ccan be absorbed as either tension or compression in one or more of theactuators 5 a, 5 b, 5 c. The displacements of the actuators 5 a, 5 b, 5c may for example be controlled such that one of the actuators, such asthe second actuator 5 b only performs a vertical displacement with nomotion component in a fore and/or aft direction, such as in thelongitudinal direction, of the vessel.

FIG. 11 shows a diagram illustrating two different angle of attackprofiles for controlling the motion, such as the heave and/or the pitch,of the fin 3 based on the conditions of the water surrounding the fin 3,such as an inflow of water or a velocity of the incoming water. Thediagram shows the pitch angle of the fin 3 during one reciprocatingmotion, such as during one stroke of the fin. The dotted line of FIG. 11illustrates an angle of attack profile optimized for a fin operating inopen water, such as when the propulsion unit is simulated without avessel. The solid line illustrates an angle of attack profile optimizedfor operation in a wake behind the vessel. Instead of the water flowmoving along the longitudinal axis of the ship, the hull of the vesselmay cause a vector of the water flow to angle upward along the rise of astern of the vessel. This generates a flow field having a verticalcomponent and an aftwards component. The boundary layer of the hull mayalso cause the flow of water to slow down, such that the flow magnitudeof the water is less than a velocity of water flowing freely withoutbeing affected by the hull of the vessel. The angle of attack profileillustrated by the dotted line takes the influence of the vessel on thewater flowing to the fin 3 into account when determining the optimalangle of attack profile for the fin. By adapting, such as optimizing,the angle of attack profile to the conditions of the water surroundingthe vessel the efficiency of the propulsion unit may be significantlyimproved.

It shall be noted that the features mentioned in the embodimentsdescribed in FIGS. 1-11 are not restricted to these specificembodiments. Any features relating to the fin, the one or moreactuators, and/or the seals of the fin comprised therein and mentionedin relation to the one or more first example embodiments of FIGS. 1 a-1b , such as dimensions of the fin and the type of actuators or sealingsolutions, are thus also applicable to the one or more second exampleembodiments described in relation to FIGS. 2-5 , and/or to the exampleembodiments described in relation to FIGS. 9-11 , and vice versa.

It shall further be noted that a vertical axis, when referred to herein,relates to an imaginary line running vertically through the ship andthrough its center of gravity, a transverse axis or lateral axis is animaginary line running horizontally across the ship and through thecenter of gravity and a longitudinal axis is an imaginary line runninghorizontally through the length of the ship through its center ofgravity and parallel to a waterline. Similarly, when referred to herein,a vertical plane relates to an imaginary plane running verticallythrough the width of the ship, a transverse plane or lateral plane is animaginary plane running horizontally across the ship and a longitudinalplane is an imaginary plane running vertically through the length of theship.

Embodiments of products (propulsion unit and vessel) according to thedisclosure are set out in the following items:

-   Item 1. A propulsion unit (1) for propelling a vessel, the    propulsion unit (1) comprising:    -   a main body (2) configured to be arranged at a keel of the        vessel and comprising a pivot point (5 a),    -   a fin (3) being movably arranged in relation to the main body        (2), and    -   an actuator assembly (4) for generating a heave motion of the        fin (3) in relation to the main body (2), the actuator assembly        (4) comprising at least one actuator (4 a, 4 b),    -   wherein the fin (3) is connected to the pivot point (5 a) such        that the fin (3) is arranged to pivot around the first pivot        point (5 a) when the at least one actuator (4 a, 4 b) generates        the heave motion of the fin (3), thereby generating a pitch        motion of the fin (3).-   Item 2. The propulsion unit (1) according to Item 1, wherein the at    least one actuator (4 a, 4 b) is a linear actuator.-   Item 3. The propulsion unit (1) according to any one of the previous    Items, wherein the propulsion unit (1) comprises at least one    actuating rod (9, 9 a, 9 b), the actuator assembly (4) being    connected to the fin (3) via the at least one actuating rod (9, 9 a,    9 b).-   Item 4. The propulsion unit (1) according to any one of the previous    Items, wherein the actuator assembly (4) is configured to be    operated with an oscillating pattern, thereby generating an    oscillating heave and pitch motion of the fin.-   Item 5. The propulsion unit (1) according to any one of the previous    Items, wherein the pivot point (5 a) is fixedly arranged to the main    body (2).-   Item 6. The propulsion unit (1) according to Item 5, wherein the    propulsion unit (1) comprises a lever arm (7), the fin (3) being    attached to the pivot point (5 a) via the lever arm (7).-   Item 7. The propulsion unit (1) according to any one of the Items 1    to 4, wherein the actuator assembly (4) comprises a first actuator    (4 a) and a second actuator (4 b), wherein the pivot point (5 a) is    connected to the second actuator (4 b) such that the pivot point (5    a) is movably arranged in relation to the main body (2).-   Item 8. The propulsion unit (1) according to Item 7, wherein the    first actuator (4 a) and the second actuator (4 b) are independently    operable in relation to each other, so that a phase difference    between the heave motion and the pitch motion of the fin (3) is    variable.-   Item 9. The propulsion unit (1) according to Item 7 or 8, wherein    the fin (3) comprises a first fin section (3 a), a second fin    section (3 b), a first connecting rod (8 a), and a second connecting    rod (8 b), wherein the first fin section (3 a) and the second fin    section (3 b) are connected via the first connecting rod (8 a) and    the second connecting rod (8 b), wherein the first connecting rod (8    a) and the second connecting rod (8 b) are arranged in parallel and    at a respective first distance and second distance from a leading    edge (10) of the first and second fin sections (3 a, 3 b).-   Item 10. The propulsion unit (1) according to Item 9, wherein the    main body (2) comprises a first through-going slot (13 a) and a    second through-going slot (13 b) for allowing the first connecting    rod (8 a) and the second connecting rods (8 b) to protrude through    the main body (3) and to be slidably arranged within the first    through-going slot (13 a) and the second through-going slot (13 b).-   Item 11. The propulsion unit (1) according to Item 9 or 10, wherein    the first connecting rod (8 a) is connected to the first actuator (4    a) and the second connecting rod (8 b) is connected to the second    actuator (4 b).-   Item 12. The propulsion unit (1) according to Item 11, wherein the    first connecting rod (8 a) and the second connecting rod (8 b) are    connected to the respective first actuator (4 a) and second actuator    (4 b) via a first actuating rod (9 a) and a second actuating rod (9    b), respectively.-   Item 13. The propulsion unit (1) according to Item 12, wherein the    first actuating rod (9 a) and the second actuating rod (9 b) are    arranged inside the main body (2).-   Item 14. The propulsion unit (1) according to any one of the Items 7    to 13, wherein the actuator assembly (4) comprises a third actuator    (4 c).-   Item 15. The propulsion unit (1) according to Item 14, wherein at    least two of the first actuator (4 a), the second actuator (4 b) and    the third actuator (4 c) are correlatively operable, to variably    adjust the pitch angle and/or the heave of the fin (3).-   Item 16. The propulsion unit (1) according to Item 14 or 15 when    dependent on any one of Items 9 to 12, wherein the fin (3) comprises    a third connecting rod, wherein the first fin section (3 a) and the    second fin section (3 b) are connected via the third connecting rod,    wherein the first connecting rod (8 a), the second connecting rod (8    b) and the third connecting rod are arranged in parallel and at a    respective first distance, second distance and third distance from    the leading edge (10) of the first and second fin sections (3 a, 3    b).-   Item 17. The propulsion unit (1) according to Item 16, wherein the    main body (2) comprises a third through-going slot (13 c) for    allowing the first connecting rod (8 c) to protrude through the main    body (3) and to be slidably arranged within the three through-going    slot (13 c).-   Item 18. The propulsion unit (1) according to Item 16 or 17, wherein    the third connecting rod (8 c) is connected to the third actuator (4    c).-   Item 19. The propulsion unit (1) according to Item 18, wherein the    third connecting rod (8 c) is connected to the third actuator (4 c)    via a third actuating rod (9 c).-   Item 20. The propulsion unit (1) according to Item 19, wherein the    third actuating rod (9 c) is arranged inside the main body (2).-   Item 21. The propulsion unit (1) according to any one of the Items 7    to 20, wherein at least one of the first actuator (4 a) and the    second actuator (4 b) is configured to be displaced in a vertical    direction.-   Item 22. The propulsion unit (1) according to Item 21, wherein the    at least one of the first actuator (4 a) and the second actuator (4    b) is restrained in a direction perpendicular to a direction of    extension of the at least one of the first actuator (4 a) and the    second actuator (4 b).-   Item 23. The propulsion unit (1) according to Item 21 or 22, wherein    the at least one of the first actuator (4 a) and the second actuator    (4 b) is restrained in a lateral and/or longitudinal direction.-   Item 24. The propulsion unit (1) according to any one of the    previous Items, wherein the propulsion unit comprises a rudder (6).-   Item 25. The propulsion unit (1) according to Item 24, wherein the    main body (2) is configured to be fixedly arranged to the keel of    the vessel, and wherein the rudder (6) is pivotably arranged to the    main body (2).-   Item 26. The propulsion unit (1) according to Item 24, wherein the    main body (2) comprises a rudder stock (11) for rotatably arranging    the main body (2) to the keel of the vessel, wherein the one or more    actuators (4 a, 4 b) and/or the at least one actuating rods (9, 9 a,    9 b) are arranged inside the rudder stock (11), and wherein the main    body (2) is configured to act as the rudder (6).-   Item 27. The propulsion unit (1) according to any one of the    previous Items, wherein the main body (2) comprises a hollow tube    (12) protruding from the main body (2) on a keel-facing side of the    main body (2), wherein the first actuating rod (9 a) and/or the    second actuating rod (9 b) is/are arranged within the hollow tube    (12), wherein the hollow tube (12) is configured to protrude into    the vessel when the main body (2) is arranged to the keel of the    vessel.-   Item 28. The propulsion unit (1) according to Item 27, wherein the    hollow tube (12) comprises a seal (14) arranged at a distal end of    the hollow tube (12) for sealing the first actuating rod (9 a)    and/or the second actuating rod (9 b) to the hollow tube (12).-   Item 29. The propulsion unit (1) according to Item 27 or 28, wherein    the rudder stock (11) is hollow and constitutes the hollow tube    (12).-   Item 30. The propulsion unit (1) according to any one of the    previous Items, wherein the fin (3) has an elliptical planform.-   Item 31. The propulsion unit (1) according to any one of the    previous Items, wherein the fin (3) comprises winglets (15).-   Item 32. A vessel (100) comprising a propulsion unit (1) for    propelling the vessel according to any one of Items 1 to 31, wherein    the main body (2) is arranged to the keel (101) of the vessel (100)    and wherein the fin is configured to perform a pitch and heave    motion in relation to the keel (101) of the vessel (100).-   Item 33. The vessel (100) according to Item 32, wherein the main    body (2) is fixedly arranged to the keel (101).-   Item 34. The vessel (100) according to Item 32, wherein the main    body (2) is rotatably arranged to the keel (101).

The use of the terms “first”, “second”, “third” and “fourth”, “primary”,“secondary”, “tertiary” etc. does not imply any particular order, butare included to identify individual elements. Moreover, the use of theterms “first”, “second”, “third” and “fourth”, “primary”, “secondary”,“tertiary” etc. does not denote any order or importance, but rather theterms “first”, “second”, “third” and “fourth”, “primary”, “secondary”,“tertiary” etc. are used to distinguish one element from another. Notethat the words “first”, “second”, “third” and “fourth”, “primary”,“secondary”, “tertiary” etc. are used here and elsewhere for labellingpurposes only and are not intended to denote any specific spatial ortemporal ordering. Furthermore, the labelling of a first element doesnot imply the presence of a second element and vice versa.

It is to be noted that the word “comprising” does not necessarilyexclude the presence of other elements or steps than those listed.

It is to be noted that the words “a” or “an” preceding an element do notexclude the presence of a plurality of such elements.

Although features have been shown and described, it will be understoodthat they are not intended to limit the claimed disclosure, and it willbe made obvious to those skilled in the art that various changes andmodifications may be made without departing from the scope of theclaimed disclosure. The specification and drawings are accordingly to beregarded in an illustrative rather than restrictive sense. The claimeddisclosure is intended to cover all alternatives, modifications, andequivalents.

LIST OF REFERENCES

-   1 propulsion unit-   2 main body-   3 fin-   3 a first fin section-   3 b second fin section-   4 actuator assembly-   4 a actuator, first actuator-   4 b second actuator-   5 a pivot point, first pivot point-   5 b second pivot point-   6 rudder-   7 lever-   8 a first connecting rod-   8 b second connecting rod-   9 actuating rod-   9 a first actuating rod-   9 b second actuating rod-   10 leading edge-   11 rudder stock-   12 hollow tube-   13 a first through-going slot-   13 b second through-going slot-   14 seal-   15 winglet-   16 trailing edge-   17 elongated slot-   18 pin-   19 elongated slot-   20 seal-   21 support surface-   100 vessel-   101 keel

What is claimed is:
 1. A propulsion unit for propelling a vessel, thepropulsion unit comprising: a main body configured to be arranged at akeel of the vessel and comprising a pivot point, a fin being movablyarranged in relation to the main body, and an actuator assembly forgenerating a heave motion of the fin in relation to the main body, theactuator assembly comprising at least one actuator, wherein the fin isconnected to the pivot point such that the fin is arranged to pivotaround the pivot point when the at least one actuator generates theheave motion of the fin, thereby generating a pitch motion of the fin.2. The propulsion unit according to claim 1, wherein the at least oneactuator is a linear actuator.
 3. The propulsion unit according to claim1, wherein the propulsion unit comprises at least one actuating rod, theactuator assembly being connected to the fin via the at least oneactuating rod.
 4. The propulsion unit according to claim 1, wherein theactuator assembly is configured to be operated with an oscillatingpattern, thereby generating an oscillating heave and pitch motion of thefin.
 5. (canceled)
 6. (canceled)
 7. The propulsion unit according toclaim 1, wherein the actuator assembly comprises a first actuator and asecond actuator, wherein the pivot point is connected to the secondactuator such that the pivot point is movably arranged in relation tothe main body.
 8. The propulsion unit according to claim 7, wherein thefirst actuator and the second actuator are independently operable inrelation to each other, so that a phase difference between the heavemotion and the pitch motion of the fin is variable.
 9. The propulsionunit according to claim 7, wherein the fin comprises a first finsection, a second fin section, a first connecting rod, and a secondconnecting rod, wherein the first fin section and the second fin sectionare connected via the first connecting rod and the second connectingrod, wherein the first connecting rod and the second connecting rod arearranged in parallel and at a respective first distance and seconddistance from a leading edge of the first and second fin sections. 10.The propulsion unit according to claim 9, wherein the main bodycomprises a first through-going slot and a second through-going slot forallowing the first connecting rod and the second connecting rods toprotrude through the main body and to be slidably arranged within thefirst through-going slot and the second through-going slot.
 11. Thepropulsion according to claim 9, wherein the first connecting rod isconnected to the first actuator and the second connecting rod isconnected to the second actuator.
 12. (canceled)
 13. The propulsion unitaccording to claim 9, wherein the first actuating rod and the secondactuating rod are arranged inside the main body.
 14. The propulsion unitaccording to claim 7, wherein the actuator assembly comprises a thirdactuator.
 15. The propulsion unit according to claim 14, wherein atleast two of the first actuator, the second actuator and the thirdactuator are correlatively operable, to variably adjust the pitch angleand/or the heave of the fin.
 16. The propulsion unit according to claim14, wherein the fin comprises a third connecting rod, wherein the firstfin section and the second fin section are connected via the thirdconnecting rod, wherein the first connecting rod, the second connectingrod and the third connecting rod are arranged in parallel and at arespective first distance, second distance and third distance from theleading edge of the first and second fin sections.
 17. The propulsionunit according to claim 16, wherein the main body comprises a thirdthrough-going slot for allowing the first connecting rod to protrudethrough the main body and to be slidably arranged within the threethrough-going slot.
 18. The propulsion unit according to claim 16,wherein the third connecting rod is connected to the third actuator. 19.The propulsion unit according to claim 18, wherein the third connectingrod is connected to the third actuator via a third actuating rod. 20.The propulsion unit according to claim 19, wherein the third actuatingrod is arranged inside the main body.
 21. (canceled)
 22. (canceled) 23.(canceled)
 24. (canceled)
 25. (canceled)
 26. (canceled)
 27. Thepropulsion unit according to claim 1, wherein the main body comprises ahollow tube protruding from the main body on a keel-facing side of themain body, wherein the first actuating rod and/or the second actuatingrod is/are arranged within the hollow tube, wherein the hollow tube isconfigured to protrude into the vessel when the main body is arranged tothe keel of the vessel.
 28. The propulsion unit according to claim 27,wherein the hollow tube comprises a seal arranged at a distal end of thehollow tube for sealing the first actuating rod and/or the secondactuating rod to the hollow tube.
 29. (canceled)
 30. (canceled) 31.(canceled)
 32. A vessel comprising a propulsion unit for propelling thevessel according to claim 1, wherein the main body is arranged to thekeel of the vessel and wherein the fin is configured to perform a pitchand heave motion in relation to the keel of the vessel.
 33. (canceled)34. (canceled)